Method for forming a hole and method for forming nozzle in orifice plate of printing head

ABSTRACT

A method for a hole inclined relative to the direction of thickness of a workpiece by light energy. A groove is formed in an energy-concentrated portion of a plate as a workpiece for opening on a major surface of a plate operating as a light energy irradiated surface for forming an irregular surface portion. The light energy is illuminated on this irregular surface portion from the major surface of the plate in an oblique direction relative to the direction of thickness of the plate. The irregular surface portion of the workpiece is formed integrally with the workpiece by injection molding. The irregular surface portion may also be formed by sand-blasting, chemical etching or by an abrasive brush. The light energy is a laser, especially an excimer laser. The workpiece may be formed of an inorganic material, an organic material or a metallic material. The hole of a larger angle of inclination is formed by employing the light energy.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a method for forming a hole inclined relativeto the direction of thickness of a workpiece by light energy. Moreparticularly, it relates to a method for forming a hole in which anirregular surface portion is formed in an energy-concentrated portion ofthe workpiece so that the light energy may be prohibited from beingreflected even in case of the incident angle of the light energyexceeding the critical angle for allowing to form a hole with a largerangle of inclination relative to the direction of thickness of theworkpiece.

2. Related Art

Recently, a so-called on-demand type printing apparatus, dispensingliquid ink drops from a nozzle responsive to recording signals forrecording on a recording medium, such as paper or films, has rapidlycome into popular use since it lends itself to reduction in size andproduction costs.

Meanwhile, a demand is recently increasing for outputting not onlyletters or pictures but also colored natural pictures similar tophotographs along with the letters or figures. In keeping with thisdemand, it has been a desideratum to print a high-quality naturalpicture, and reproduction of a half-tone has become critical.

For enabling reproduction of the half-tone, the present inventors haveproposed a printing head,in which the density of dots printed may becontrolled by discharging an ink solution obtained on mixing the ink anda diluting solution and by varying the density of the ink solution forprinting the natural picture without deteriorating the resolution.

Such printing head is made up of a portion adapted for applying theforce of discharging the ink or the diluting solution to the ink or thediluting solution, such as an ink reservoir or a diluting solutionreservoir, having a piezo-element or a heating element, and a nozzleportion (so-called orifice plate) for guiding the discharging of the inkor the diluting solution.

The orifice plate is formed with a through-hole operating as an inknozzle and another through-hole operating as a nozzle for a dilutionsolution. These two through-holes are of extremely small diameters.

Thus, these through-holes are difficult to form with a boring machine ora drill since there is a limit on the minimum size and accuracy inopening size cannot be maintained if plural through-holes are to beformed due to wear produced in the cutting chips. The through-holes arealso difficult to form using an ultrasonic cutting method.

It may be envisaged to form these through-holes by techniques such asreactive ion etching (RIE) or ion milling employed in a semiconductorproduction process. These techniques are however inappropriate since aworkpiece of a thickness sufficient for use as an orifice plate can beworked by this technique only by an extremely time-consuming operation.

The present inventors have proposed in Japanese patent Application No.7-88999 an orifice plate in which at least one of a through-holeoperating as an ink nozzle and a second through-hole operating as athrough-hole for the dilution solution are formed obliquely relative tothe direction of thickness of the orifice plate. However, It is howeverextremely difficult to form the through-hole obliquely by a methodemploying a boring machine or a drill or by an ultrasonic method.

Thus the through-hole in an orifice plate, which is small in diameterand which needs occasionally to be formed obliquely, is formed byilluminating the light energy, such as that of a laser. Since the lasercan be reduced in beam diameter and radiation diameter, it is suited toformation of a hole with a small diameter. As laser, carbon dioxide gaslaser or a YAG laser may be employed in addition to an excimer laser.

In laser working, a laser beam having the same angle of inclination asthat of the through-hole to be formed is illuminated from the workpiecesurface for forming the through-hole in the proceeding direction of thelaser beam.

OBJECT AND SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide a methodfor forming a through-hole having a larger angle of inclination using alight energy.

In one aspect, the present invention provides a method for forming ahole including forming an irregular surface portion in anenergy-concentrated portion of a workpiece, and radiating the lightenergy on the irregular surface portion for forming a hole inclinedrelative to the direction of thickness of the workpiece.

In another aspect, the present invention provides a method for forming anozzle in an orifice plate for a printing head including irradiating anirregular surface portion of the surface of the orifice plate with alight energy for forming a hole inclined at a pre-set angle relative tothe direction of thickness of the orifice plate.

In still another aspect, the present invention provides a method forforming a first nozzle in an orifice plate for a printing head includingforming a first nozzle inclined at a pre-set angle relative to thedirection of thickness of the orifice plate and forming a second nozzlenormal to the direction of thickness of the orifice plate in adjacencyto the first nozzle. The first and second nozzles are formed byirradiation with a light energy and at least the portion in which thefirst nozzle is formed is formed with an irregular surface portionbefore being irradiated with the light energy.

The irregular surface portion of the workpiece is formed integrally withthe workpiece by injection molding.

The irregular surface portion may also be formed by sand-blasting,chemical etching or by an abrasive brush.

The light energy is a laser, especially an excimer laser.

The workpiece may be formed of an inorganic material, an organicmaterial or a metallic material.

The method for forming the hole according to the present invention issuited for forming a through-hole in an orifice plate. The thickness ofthe hole-forming portion of the workpiece is preferably 15 to 200 μm.

In the hole-forming method of the present invention, in which theirregular surface portion is provided in the energy-concentrated portionof the workpiece, and the light energy is radiated on this irregularsurface portion, there is formed a wall lying in the path of thereflected light energy, or the state of light energy engagement may beimproved. Thus the angle of inclination of the light energy may beimproved and working is started for forming a hole inclined relative tothe direction of thickness of the workpiece while there is no risk oflight reflection even for an incident angle larger than the workingcritical angle.

If the irregular surface portion of the workpiece is integrally formedwith the workpiece by injection molding, a large number of workpiecesmay be worked simultaneously, thereby improving the productivity.

If the irregular surface portion is formed by sand-blasting or chemicaletching or using an abrasive brush, the irregular surface portion isworked as fine-sized irregular surface portions.

If the laser is employed as the light energy, small-diameter holes maybe formed. In addition, if the excimer laser is employed as the laser,working may be performed without thermally affecting the workpiece, sothat only the portion irradiated with the laser light beam can be workedto high quality.

With the method for forming the orifice plate employing the hole formingmethod according to the, present invention, since the irregular surfaceportion is formed in the energy-concentrated portion of the plate as aworkpiece, and the light energy is radiated on this irregular surfaceportion, the working by light energy may be facilitated. Working may beinitiated without light reflection even for the light incident angleexceeding the working critical angle, so that a through-hole may beformed which has an inclination angle relative to the direction of platethickness exceeding the working critical angle of the light energy.

If the irregular surface portion of the plate is formed bysand-blasting, chemical etching or an abrasive brush, the irregularsurface portion is formed as plural irregular surface portions.

If the laser is used as the light energy in the above-describedembodiment, small-diameter holes may be worked easily. If the excimerlaser is used as the laser, the workpiece may be worked without beingthermally affected so that high-quality working may be achieved only atthe laser light irradiated portion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing an orifice plate produced by amethod for producing an orifice plate according to the presentinvention.

FIG. 2 is a plan view showing an orifice plate produced by a method forproducing an orifice plate according to the present invention.

FIG. 3 schematically shows sequential operations of a printing heademploying a produced orifice plate and the state in which a meniscus isformed on the produced orifice plate.

FIG. 4 schematically shows sequential operations of a printing heademploying a produced orifice plate and the state in which the ink hasbeen extruded out of the through-hole.

FIG. 5 schematically shows sequential operations of a printing heademploying a produced orifice plate and the state in which the dilutionsolution has been extruded out of the through-hole to form an inksolution.

FIG. 6 schematically shows sequential operations of a printing heademploying a produced orifice plate and the state in which the inksolution has been grown in a columnar shape.

FIG. 7 schematically shows sequential operations of a printing heademploying a produced orifice plate and the state in which a constrictionhas been produced in the columnar-shaped ink solution.

FIG. 8 schematically shows sequential operations of a printing heademploying a produced orifice plate and the state in which the inksolution about to start its flight.

FIG. 9 schematically shows sequential operations of a printing heademploying a produced orifice plate and the state in which the inksolution has flown into air.

FIG. 10 shows a process step in an illustrative method for producing anorifice plate employing a method for producing an orifice according tothe present invention, showing the state in which a groove is formed inthe orifice plate.

FIG. 11 shows a process step in an illustrative method for producing anorifice plate employing a method for producing an orifice according tothe present invention, showing the state in which the light energy isbeing radiated for forming a second through-hole in a plate.

FIG. 12 shows a process step in an illustrative method for producing anorifice plate employing a method for producing an orifice according tothe present invention, showing the state in which the light energy isbeing radiated for forming a first through-hole in a plate.

FIG. 13 shows a process step in an illustrative method for producing anorifice plate employing a method for producing an orifice according tothe present invention, showing the state in which the first through-holehas been formed in a plate.

FIG. 14 shows a process step in an illustrative method for producing anorifice plate employing a method for producing an orifice according tothe present invention, showing the completed state of the orifice plate.

FIG. 15 shows a modification of the method for producing the orificeplate employing a method for forming an orifice plate according to thepresent invention, and showing the state in which the light energy isbeing radiated for forming first and second through-holes in a plate.

FIG. 16 shows a process step in a second modification of the method forproducing the orifice plate employing a method for forming an orificeplate according to the present invention, and showing the state in whicha groove is being formed in a plate.

FIG. 17 shows a process step in the second modification of the methodfor producing the orifice plate employing a method for forming anorifice plate according to the present invention, and showing the statein which a hole has been formed in the bottom of the groove formed inthe plate.

FIG. 18 shows a process step in the second modification of the methodfor producing the orifice plate employing a method for forming anorifice plate according to the present invention, and showing the statein which a first through-hole has been formed in the plate.

FIG. 19 shows a process step in the second modification of the methodfor producing the orifice plate employing a method for forming anorifice plate according to the present invention, and showing the stepof roughing the plate surface.

FIG. 20 shows a process step in the second modification of the methodfor producing the orifice plate employing a method for forming anorifice plate according to the present invention, and showing the stateof radiating the light energy on a plate.

FIG. 21 shows a process step in the second modification of the methodfor producing the orifice plate employing a method for forming anorifice plate according to the present invention, and showing the statein which holes are being formed in the proximal portions of protrusionsformed on a plate.

FIG. 22 shows a process step in the second modification of the methodfor producing the orifice plate employing a method for forming anorifice plate according to the present invention, and showing the statein which a first through-hole has been formed in the proximal portionsof protrusions formed on a plate.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, preferred embodiments of the presentinvention will be explained in detail. In the present embodiment, themethod for forming a hole according to the present invention is appliedto production of an orifice plate.

FIG. 1 shows an orifice plate 11 prepared in the instant embodiment. Theorifice plate 11 has a pair of through-holes 1, 2 extending from itsmajor surface 11a to the other major surface 11b. The opening ends ofthe through-holes 1, 2 on the major surface 11a serve as liquid supplyports 1a, 2a, while the opening ends of the through-holes 1, 2 on theopposite major surface 11b serve as liquid discharge ports 1b, 2b.

The through-hole is formed obliquely through the orifice plate 11 at aninclination relative to the thickness of the orifice plate 11, while thethrough-hole 1 is formed parallel to the thickness of the orifice plate.The through-holes 2 and 1 are referred to hereinafter as first andsecond through-holes, respectively. The first through-hole 2 approachesthe liquid discharge port 1b of the through-hole 1 in a directionproceeding towards the liquid discharge port 2b.

In the above-described orifice plate, the first through-hole 2 and thesecond through-hole 1 serve as nozzles for the ink and for the dilutionsolution, respectively.

In the above-described orifice plate, the first through-hole 2 and thesecond through-hole 1 are reduced in cross-section in a directionproceeding from the liquid supply ports 2a, 1a towards the liquiddischarge ports 2b, 1b, respectively, as shown in Figs.1 and 2. That is,if the cross-sectional areas of the liquid supply ports 2a, 1a of thefirst and second through-holes 2, 1 are S2a, S1a, respectively, and thecross-sectional areas of the liquid discharge ports 2b, 1b thereof areS2b, S1b, respectively, the relation S2b<S2a and the relation S1b<S1ahold.

The thickness of the orifice plate is selected to be 15 to 100 μm forstabilizing the flight direction of liquid droplet and for withstandingthe elevated liquid pressure.

A printing head employing the orifice plate produced in the instantembodiment is now explained. The printing head is of a carrier jet typein which a box-shaped ink reservoir 16 filled with an ink 6 is arrangedin the liquid supply port 2a of the first through-hole 2 and abox-shaped dilution solution reservoir 15 filled with a dilutionsolution 5 is arranged in the liquid supply port 1a of the secondthrough-hole 1, as shown in FIG. 3. A heating element 3 and anotherheating element 4 are arranged on a bottom surface 15a of the dilutionsolution reservoir 15 and on a bottom surface 16a of the ink reservoir16, respectively.

For printing by the printing head, the ink 6 charged into the inkreservoir 16 is charged into the first through-hole 2 by a capillaryphenomenon for forming a first meniscus M2, while the dilution solution5 charged into the dilution solution reservoir 15 is charged into thesecond through-hole 1 by a capillary phenomenon for forming a secondmeniscus M1, as shown in FIG. 3.

A voltage pulse is then supplied to the heating element 4 arranged onthe bottom surface 16a of the ink reservoir 16 for heating the ink 6within the ink reservoir 16 for producing a bubble B2 at a positionregistering with the heating element 4. The pressure within the inkreservoir 16 and hence the pressure within the first through-hole 2 arethen raised, so that the ink 6 within the through-hole 2 is extruded anddeposited as a droplet on the major surface 11b of the orifice plate 11,as shown in FIG. 4. The amount of the extruded ink 6 depends upon thepulse width or the voltage value of the voltage pulse supplied to theheating element 4.

A voltage pulse is then applied to the heating element 3 arranged on thebottom surface 15a of the dilution solution reservoir 15 for heating thedilution solution 5 in the dilution solution reservoir 15 for generatinga bubble B1 at a position registering with the heating element 3, asshown in FIG. 5. The pressure within the dilution solution reservoir 15and hence the pressure within the second through-hole 1 are then raised,so that the dilution solution 5 within the through-hole 1 is extruded atthe liquid discharge port 1b so as to be unified with the droplet of theink 6 deposited on the major surface 11b of the orifice plate 11 to forman ink solution 7 in the form of a droplet, as shown in FIG. 5.

If the voltage pulse ceases to be supplied to the heating element 4 ator before this time, the bubble B2 vanished rapidly, so that theinternal pressure within the ink reservoir 16 and the first through-hole2 is lowered. This strips the ink solution 7 from the ink 6, as shown inFIG. 6, with the ink 6 being receded into the first through-hole 2 foragain forming a meniscus M2. The ink solution 7 grows in a column shape.

The voltage pulse to the heating element 3 is then terminated. Thebubble B1 then vanished quickly, as shown in FIG. 7, thus lowering thepressure within the dilution solution reservoir 15 and within the secondthrough-hole 1 to recede the dilution solution 5 into thethrough-hole 1. This produces a constriction 7a at the side of theliquid discharge port 1b of the ink solution 7.

As the bubble B1 is further reduced in size, flight of the ink solution7 starts, as shown in FIG. 8, until the ink solution 7 flies into air,as shown in FIG. 9. The ink solution 7 becomes deposited on a recordingmedium to effect printing.

The density of the ink solution 7, which is a mixture of the ink and thedilution solution, is determined by the amount of the ink 6 extrudedfrom the first through-hole 2, and may be controlled by the amplitude orthe width of the voltage pulse applied to the heating element 4. If theamplitude or the width is increased or decreased, the amount of the ink6 is increased or decreased, respectively, thus varying the density ofthe ink solution 7. The amplitude or width of the voltage pulse may bevaried in a range determined by experiments to an optimum value.

The above-described sequence of operations in the printing head ismerely exemplary and the timing or states of the respective operations,such as the shape or the charging performance of the ink solution, arevaried with structural elements, such as the size of the liquiddischarge ports, physical elements, such as viscosity or surface tensionof the ink or the dilution solution, or operating conditions, such asdischarging frequency.

The method for producing the orifice plate employing the method forforming a hole according to the present invention is explained.

First, a plate 31 which is to be an orifice plate is provided. In thepresent embodiment, the plate is formed of an organic material, such ashigh molecular material, and is produced by injection molding. In thepresent embodiment, when forming the plate 31, as a workpiece, byinjection molding, a groove 41 opened on a major surface 31a of theplate 31 as a light irradiated surface is formed, as shown in FIG. 10.This groove 41 is formed at a energy-concentrated portion of the plateirradiated with the light energy for forming an obliquely extendingthrough-hole.

The groove 41 is substantially U-shaped in cross-section and has aninclined lateral side 41a lying along the light energy proceedingdirection.

The light energy, such as a laser light energy, is radiated from themajor surface 31a of the plate 31, along the thickness of the plate 31,as indicated by arrow M1 in FIG. 11. As the laser, enumerated by anexcimer laser, a carbon dioxide laser or a YAG laser, the excimer laseris herein employed.

If the excimer laser is employed for working, molecular bondage issevered for vaporizing and removing substances by a working termedablation, thus reducing thermal effects encountered in conventionalthermal working and assuring high-quality working of only portionsirradiated with the laser beam.

This produces a second through-hole 32 traversing the plate 31 along itsthickness from its major surface 31a to its opposite major surface31bwith an opening end 32a on the major surface 31a and an opening end32b on the major surface 31b operating as a liquid supply port and as aliquid discharge port, respectively. Since the second through-hole 32 isformed by laser radiation, the through-hole 32 has a cross-sectionalarea S32a on the major surface 31a on the light energy incident sidewhich is larger than a cross-sectional area S32b on the opposite majorsurface side 31b, so that the relation S32b<S32a holds.

The light energy, such as the laser light energy, is radiated from themajor surface 31a of the plate 31 obliquely relative to the direction ofthickness thereof, as shown in FIG. 12. The light energy radiatingdirection is set so as to approach the opening 32b, that is the liquiddischarge port of the second through-hole 32, in a direction proceedingfrom the major surface 31a towards the major surface 31b. As the laser,enumerated by an excimer laser, a carbon dioxide laser or a YAG laser,the excimer laser is again employed.

Since the groove 41 is formed in the instant embodiment as an irregularsurface portion in an energy-concentrated portion in the plate 31, thatis a workpiece, in which the obliquely directed light energy isconcentrated for forming the obliquely extending through-hole in theplate 31, the light energy indicated by arrow M2 in FIG. 10 is radiatedon the inclined lateral side 41a of the groove 41.

Since the lateral side 41a is an inclined surface, the light energyindicated by arrow M2 is incident on the lateral side 41a at an angleclose to a right angle. The incident light proceeds along a straightpath for working.

This produces a first through-hole 33 traversing the plate 31 along itsthickness from its major surface 31a to its opposite major surface 31b,with an opening end 33a on the major surface 31a and an opening end 33bon the major surface 31b operating as a liquid supply port and as aliquid discharge port, respectively, thus completing an orifice platehaving the obliquely extending first through-hole 33 and the secondthrough-hole 32 extending along the thickness thereof, as shown in FIG.14.

Since the first through-hole 33 is formed by excimer laser irradiation,the cross-sectional area S33a thereof on the major surface 31a on thelight energy incident side becomes larger than the cross-sectional areaS33b on the opposite major surface 31b, so that the relation S33b<S33aholds. The first through-hole 33 is formed so that the opening end 32bas the liquid discharge port of the second through-hole 33 is approachedin a direction proceeding towards the opening 33b as the liquiddischarge port.

Although the first through-hole is formed in the above-describedproduction method after formation of the second through-hole, the lightenergies employed in the above-described production method, indicated byarrows M1 and M2, may be radiated simultaneously from the major surface31a of the plate 31 for simultaneously forming the first and secondthrough-holes in the orifice plate.

Although the groove having a substantially U-shaped cross-section, andhaving an inclined surface lying in the light path of the light energy,is formed in the plate 31, that is a workpiece, in the above-describedproduction process for providing an irregular surface portion on theenergy-concentrated portion of the plate 31, the irregular surfaceportion may also be formed as a groove 51 of a U-shaped cross-sectionopening on the major surface 31a operating as a light energy irradiatedsurface.

If the light energy as indicated by arrow M2 in FIG. 16 is radiated fromthe major surface 31a of the plate 31 formed with such groove 51, thelight energy is reflected in a direction opposite to the incidentdirection. However, it is leaped back by a lateral side 51a operating asa wall. Thus the working is started at this portion to form a small hole52 on the bottom surface of the groove 51, as shown in FIG. 17, forenhancing the engagement of the light energy with the workpiece forstarting the working in the light energy incident direction. Thisproduces a first through-hole 33 traversing the plate 31 along itsthickness from its major surface 31a to its opposite major surface 31b,with an opening end 33a on the major surface 31a and an opening end 33bon the opposite major surface 31b operating as a liquid supply port andas a liquid discharge port, respectively. The light energy may be alaser beam enumerated by an excimer laser, a carbon dioxide laser or aYAG laser. The excimer laser is employed for the above reason.

In the above-described production method, the irregular surface portionis formed simultaneously with formation of the plate by injectionmolding. It is however possible to form the vicinity of the irregularsurface portion of the plate by injection molding and to bond theresulting portion to a plate portion forming the remaining plate portionfor ultimately forming the irregular surface portion in the completedplate. The portion inclusive of the irregular surface portion and themain plate portion may be formed of the same material or differentmaterials.

In the above-described producing method, the surface of the plate 31 asthe workpiece is formed with a groove for forming the irregular surfaceportion. Alternatively, the plate surface may be roughed for forming theirregular surface portion in the energy-concentrated portion.

In such case, a plate 61 which is to be an orifice plate is provided. Inthe instant embodiment, the plate 61 is formed of an organic material,such as a high molecular material. Specifically, the plate is apolyimide film.

Then, a major surface 61a of the plate 61, which is to be irradiatedwith the light energy, as shown in FIG. 19, is roughed by asand-blasting method consisting in colliding fine particles against aworkpiece energetically for physically scraping the workpiece surface bythese particles. By roughing the substantially smooth polyimide surface,having a maximum height of surface irregularities amounting to tens ofAngstroms, by the sand-blasting method, fine-sized irregularities withthe maximum height on the order of five μm, are formed.

The light energy indicated by arrow M2 is radiated from the majorsurface 61a of the plate 61, as shown in FIG. 19. The incident lightenergy is collided against protrusions 62 formed by sand-blasting on themajor surface 61a of the plate 61 and thereby trapped to initiateworking thereat as shown in FIG. 20. Thus, small holes 63 are formed atthe proximal portions of the protrusions 62 as shown in FIG. 21 forenhancing the engagement of the light energy with the workpiece forstarting the working in the light energy incident direction. Thisproduces a first through-hole 33 traversing the plate 61 along itsthickness from its major surface 61a to its opposite major surface 61b,with an opening end 33a on the major surface 61a and an opening end 33bon the opposite major surface 61b operating as a liquid supply port andas a liquid discharge port, respectively.

A polyimide film whose surface was left intact and another polyimidefilm whose surface was worked by sand-blasting as described above wereworked as described above for forming obliquely extending holes. It wasfound that, with the polyimide film whose surface was left intact andthe polyimide film whose surface was worked by sand-blasting and therebyroughed as described above, a hole having an inclination angle of amaximum of 80° and a hole having an inclination angle of a maximum of85° could be formed, respectively.

The light energy may be a laser beam enumerated by an excimer laser, acarbon dioxide laser or a YAG laser. The excimer laser is preferred forthe above reason.

Although the plate surface is roughed by sand-blasting with theabove-described producing method, the plate surface may also be roughedby a chemical etching method or a method employing an abrasive brush.

Although the organic materials, such as high molecular materials, areemployed in the above-described embodiments as the material of the plateas the workpiece, organic materials or metals may also be employed asplate materials.

What is claimed is:
 1. A method for forming a hole in a workpiececomprising the steps of providing a workpiece having a thicknessdimension: forming an irregular surface portion in a surface portion ofthe workpiece, and radiating light energy on the irregular surfaceportion at an angle so as to form an elongate hole in the workpiecewhich is inclined relative to the thickness direction of the workpiece.2. The method for forming a hole as claimed in claim 1 wherein theirregular surface portion in the workpiece is integrally formed byinjection molding of the workpiece.
 3. The method for forming a hole asclaimed in claim 1 wherein the irregular surface portion in theworkpiece is formed by sand-blasting.
 4. The method for forming a holeas claimed in claim 1 wherein the irregular surface portion in theworkpiece is formed by chemical etching.
 5. The method for forming ahole as claimed in claim 1 wherein the irregular surface portion in theworkpiece is formed using an abrasive brush.
 6. The method for forming ahole as claimed in claim 1 wherein the light energy is a laser.
 7. Themethod for forming a hole as claimed in claim 6 wherein the laser is anexcimer laser.
 8. The method for forming a hole as claimed in claim 1wherein the workpiece is an organic material.
 9. The method for forminga hole as claimed in claim 1 wherein the workpiece is an inorganicmaterial.
 10. The method for forming a hole as claimed in claim 1wherein the workpiece is a metallic material.
 11. The method for forminga hole as claimed in claim 1 wherein the workpiece adjacent the elongatehole has a thickness ranging between 15 μm and 200 μm.
 12. The methodfor forming a hole as claimed in claim 11 wherein the workpiece is anorifice plate.
 13. A method for forming a nozzle in a orifice plate fora printing head comprising the steps of:providing an orifice platehaving a thickness dimension and having an irregular surface portion:irradiating the irregular surface portion of the orifice plate withlight energy at an angle so as to form an elongate hole inclined at apre-set angle relative to the direction of the thickness of the orificeplate.
 14. A method for forming a first nozzle in an orifice plate for aprinting head comprising:forming a first nozzle inclined at a pre-setangle relative to the direction of thickness of the orifice plate; andforming a second nozzle normal to the direction of thickness of theorifice plate in adjacent to said first nozzle; wherein said first andsecond nozzles are formed by irradiation with a light energy and atleast the portion in which the first nozzle is formed is formed with anirregular surface portion before being irradiated with said lightenergy.
 15. A method of forming holes in a workpiece comprising thesteps of:providing a workpiece having a thickness dimension and havingan irregular surface portion; forming a first elongate hole extendingthrough the workpiece at a first angular orientation generally normal tothe thickness dimension adjacent the irregular surface portion; forminga second elongate hole at the irregular surface portion extendingthrough the workpiece at a second different angular orientation; saidfirst and second elongate holes being formed by laser light irradiation.